A Whole Spectrum Of Change Is Upon Us And It’s Far More Than Channel 38...
July 2011 Issue 143
Chris Headlam, MD of Orbital Sound, makes a wake-up call to everyone involved in theatre and live event sound, offering practical recommendations for the use of wireless technology.
Change is in the air. And there’s a strong breeze coming our way. We’ve all been aware for some time that Channel 69 will cease to be an option for radio microphone operation as of next year. Hopefully, that’s not news for most of us – the majority of venues and users affected by this
change are already aware of the implications and are making plans accordingly. Or they certainly should be. However, less commonly known are the rest of the changes: the range of kit and the frequency slots that will also cease to be functional by the end of next year at the latest. That leaves very little time for planning budgets and selecting replacement kit. The situation is further complicated by the probable imminent emergence of white space devices, which use cognitive radio technology to frequency-hop around seemingly unoccupied channels to maintain their communications.
The finite RF spectrum is becoming progressively overpopulated. Our industry must have its fair slice of the spectrum pie; otherwise its ability to handle the range of live event projects that it currently delivers will be severely compromised. Do any of us want to face a situation where a show has to be written to suit the number of channels that are likely to be available at a particular venue? “Sorry, no point in you writing that multi-part harmony into this show, as we won’t have enough spectrum to go round!” That sounds absurd but, in certain venues, it’s going to be a very real possibility.
GOOD NEWS, FOR SOME
Yes, there is some good news – but only for those who were sufficiently informed to fulfill three vital conditions:
1. Be lucky enough to understand the Ofcom rules about the move from Channel 69, and can prove their ownership by dredging up their original purchase records (despite the fact that there was no real reason to have
kept them in safe storage all this time).
2. Be fortunate enough to know that they had to buy a Channel 69 licence for their kit in the first place – many did not, which is not altogether surprising as there was no requirement from Ofcom for manufacturers to mark their packaging accordingly. In our broad estimation, approximately 75% of users never bought a licence – many of them were unaware they had to – and were consequently unable to submit a claim. An unfortunate economic mistake, when a two year
licence for the whole Channel 69 band currently only costs a tad over £100.
3. Be quick on the uptake, having submitted their paperwork before the end of last year, in time to claim a 55% compensatory rebate on
their old Channel 69 stock.
BAD NEWS ON THE WAY...
The bad news stems from a number of causes, and the main casualties will be the users of radio comms equipment. They have to move to an area of spectrum with very limited real estate. Our live event industry needs the freedom to deploy radio microphones and in-ear monitoring (IEM) systems, as well radio comms, exactly where and when it needs, with each component playing a critical part in the success of a production.
The demise of Channel 69 will see Channel 38 as the alternative, but we can’t fit everything in. So, how do the available frequencies measure up? Channel 38 is semi ring-fenced for Programme Making and Special Event (PMSE) applications, but you still need to buy a licence.
We share Channels 39 through 60 with digital television but there are regional variations. It therefore depends on which part of country you
are working in, as to which part of the spectrum you can use – planning a tour will become even more complex, as the amount of interleaved
spectrum (the segments we share with TV) has decreased by almost 40%. We will be sharing these channels, or segments within them, with
analogue radio comms and IEM.
With most kit, you can squeeze around 15 channels into Channel 38 – sometimes this will be enough, but a big show for example, might use two radio mic channels, 12 channels of IEM, as well as eight channels of analogue duplex radio comms. That would be right on the maximum limit of what’s practically available, and damn near impossible in places such as Edinburgh and Tunbridge Wells, where the predicted availability of interleaved spectrum is sparse.
THE RADIO COMMS CONUNDRUM
Radio comms equipment that currently uses the “C6” frequencies will be in trouble. These frequencies - Channels 32 and 33 - will not be
licensable or usable in the UK by the tail end of 2012. Internationally, the situation is further complicated by the lack of consistency in the
channel numbering, due to the fact that TV channels vary in bandwidth in different parts of the world and so have different spacing.
For example, TV channels are eight MHz wide in the UK, but can be only six or seven MHz wide in other territories. Can we simply get the equipment re-chipped? Perhaps, but deciding on the choice of channels for rechipping is the problem. If the kit could be rechipped to something other than Channel 38, then it presumes the customer will get a licence.
If you re-chip into Channel 38, at least it will work, but that’s where the radio mics are going.
So if you re-chip into another band or channel, and then find out that you or your customer can’t get a licence, you’re still screwed. Any radio comms kit using the “A2” channels, in the middle of UK Channels 41, 42
and 43, will also be in the primary bands for radio mics when channel 38 is full. A show’s first 15 radio mic channels will fit into Channel
38’s eight MHz of bandwidth, but the amount you can fit into the adjacent channels is fewer due to the intermodulation products from
Channel 38. With a large production’s radio mics and in-ear monitors swiftly filling up Channel 38 and more, where on earth do you fit in radio comms? Effectively, there’s no room at the Inn.
SOLUTIONS AND SYNCHRONICITY
Our best-hope solution is to get as many frequencies as possible outside the Channel 38 area, but the technology to do this on a wide scale is likely to be several years away.
Ultimately, we might need to push radio mics and in-ear monitors – both of which need sufficient RF bandwidth to deliver full-range 20Hz to 20kHz audio performance – up into the GHz bands. Yet at the very least, we must get radio comms out of this range now. Fortunately, this
application doesn’t require full-range, 20-20 performance, and around 12kHz of audio bandwidth is sufficient for good intelligibility. It is therefore not so hungry in terms of RF bandwidth.
Although it’s important to keep communications synchronous (i.e. free from time delays) across multiple users, it’s nowhere near as critical as with radio mics. A few milliseconds delay with radio comms is not too
much of an issue. Radio mics, however, have to be totally synchronous, with absolutely linear transmission – when an analogue system starts transmitting, nothing can get in the way. You can’t store it, error-correct it and feed it forward, then reconstitute the analogue like you can with
digital, and even a small time delay is instantly noticeable to an audience, which can quickly make the situation unworkable.
Radio comms doesn’t suffer from this, and can work digitally in a slice of RF bandwidth that would be performance restricting to radio mics. Given the forthcoming spectrum changes, digital is the only practical route forward for comms, to give us usability after the end of 2012. Going digital with radio comms has some very positive spin-offs, especially in the 2.4GHz band. This is a licence-free radio frequency band worldwide, so a single piece of kit can be used internationally without reconfiguring. Plus, as it’s an international standard, even Ofcom is unlikely to sell it off for TV usage to the likes of Mr Murdoch...
It is important not to confuse 2.4GHz with WiFi, which although a subset of 2.4GHz, is purely a networking standard. If you used WiFi for any of the applications in question, you would share your communications with the world’s computers – not recommended!
We should strive to position radio comms solely in the 2.4GHz band. The space we will have available for radio mics and IEMs is precious enough, without having to squeeze radio comms into the same channels. Lastly, start to panic if you need to take a large tour, theatre production or conference into Edinburgh, Tunbridge Wells and possibly other towns and cities. There really won’t be enough channels.
WHITE SPACE DEVICES
We need to keep an eye on the issue of white space broadband - a further challenge to our spectrum. Often referred to as “WiFi on
Steroids”, this is an emerging technology that is targeting the so-called “white spaces” of unused TV broadcasting spectrum. Traditionally
left empty to avoid interference between broadcast channels, these as yet unlicensed patches of spare spectrum are up for grabs by very large and hungry organisations. White space devices will harness these areas of spectrum for mobile networking and rural broadband, with WiFi transmitters aiming for a range of around 10km. That is orders of
magnitude beyond the usual WiFi hot spots.
The same technology is also targeting machine-to-machine communication. Will this affect the live event industry? Watch this space. In the days before this article went to press, the Cambridge TV White Spaces Consortium, which includes the likes of BBC, BSkyB, BT, Microsoft, Nokia and Samsung, announced a proof of concept trial around Cambridge, UK. We await news of the outcome. The implications are large and very mass-market.
How might this affect us? The technology will apparently work across a wide range of frequency bands, in a relatively uneducated manner. Instead of working as an intelligent device, looking for a completely open frequency and jumping to it, it works a different way round; it jumps on a frequency and if that’s busy, it hops to another one and so on, until it finds a free one. In effect, it’s an RF grasshopper – imagine a field of the things! – hopping from frequency to frequency, and nudging packets of data out of the way. With pure data, a series of delays in the packets is not a huge issue, but what if the data is carrying real-time audio?
It may be that the only real long-term solution is to make all radio microphone systems digital, but that cannot happen overnight and certainly not for an estimated decade if ever at all, as both the technology and economics are not a current reality. In pure audio production terms, we don’t need them to be digital. In absolute
terms, analogue works just fine but we can make a start with radio comms, and take that into the digital realm first. In the meantime, we
hope that the digital grasshopper won’t give us a hard time, and that we can use intelligent radio microphone technology – such as Shure’s Axient, and digital radio comms equipment from the likes of Clear-Com or HME that operates on 2.4GHz – as part of our get-out-of jail